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Shifts in densities of apex predators may indirectly affect fundamental ecosystem processes, such as decomposition, by altering patterns of cascading effects propagating through lower trophic levels. These top–down effects may interact with anthropogenic impacts, such as climate change, in largely unknown ways. We investigated how changes in densities of large predatory arthropods in forest leaf-litter communities altered lower trophic levels and litter decomposition. We conducted our experiment in soil communities that had experienced different levels of long-term average precipitation. We hypothesized that altering abundances of apex predators would have stronger effects on soil communities inhabiting dry forests, due to lower secondary productivity and greater resource overexploitation by lower trophic levels compared to wet forests. We experimentally manipulated abundances of the largest arthropod predators (apex predators) in field mesocosms replicated in the leaf-litter community of Iberian beech forests that differed in long-term mean annual precipitation by 25% (three dry forests with MAP 1,400 mm). After one year, we assessed abundances of soil fauna in lower trophic levels and indirect impacts on leaf-litter decomposition using litter of understorey hazel, Corylus avellana. Reducing densities of large predators had a consistently negative effect on final abundances of the different trophic groups and several taxa within each group. Moreover, large predatory arthropods strongly impacted litter decomposition, and their effect interacted with the long-term annual rainfall experienced by the soil community. In the dry forests, a 50% reduction in the densities of apex predators was associated with a 50% reduction in decomposition. In wet forests, the same reduction in densities of apex soil predators did not alter the rate of litter decomposition. Our results suggest that predators may facilitate lower trophic levels by indirectly reducing competition and resource overexploitation, cascading effects that may be more pronounced in drier forests where conditions have selected for greater competitive ability and more rapid resource utilization. These findings thus provide insights into the functioning of soil invertebrate communities and their role in decomposition, as well as potential consequences of soil community responses to climate change., This study has been funded by Spanish Ministry of Science and Innovation grants CGL2010‐18602, CGL2015‐66192‐R and Andalusian grant P12‐RNM‐1521‐EEZA to J.M.L.; the European Regional Development Fund, Agencia Nacional de la Promoción de Ciencia y Tecnología (PICT 2016‐1780), Argentina to A.T.A.; and FPI fellowship (BES‐2011‐043505) to N.M.‐R.

The promotion of native vegetation as a habitat for natural enemies, which could increase their abundance and fitness, is especially useful in highly simplified settings such as Mediterranean greenhouse landscapes. Spiders as generalist predators may also be involved in intra-guild predation. However, the niche complementarity provided by spiders as a group means that increased spider diversity may facilitate complementary control actions. In this study, the interactions between spiders, the two major horticultural pests, Bemisia tabaci and Frankliniella occidentalis, and their naturally occurring predators and parasitoids were evaluated in a mix of 21 newly planted shrubs selected for habitat management in a highly disturbed horticultural system. The effects of all factors were evaluated using redundancy analysis (RDA) and the generalized additive model (GAM) to assess the statistical significance of abundance of spiders and pests. The GAM showed that the abundance of both pests had a significant effect on hunter spider’s abundance, whereas the abundance of B. tabaci, but not F. occidentalis, affected web-weavers’ abundance. Ordination analysis showed that spider abundance closely correlated with that of B. tabaci but not with that of F. occidentalis, suggesting that complementarity occurs, and thereby probability of biocontrol, with respect to the targeted pest B. tabaci, although the temporal patterns of the spiders differed from those of F. occidentalis. Conservation strategies involving the establishment of these native plants around greenhouses could be an effective way to reduce pest populations outdoors., The study was supported by the RECUPERA 2020 Project funded by the Spanish MINECO and EU-FEDER program, by TRANSFORMA (PP.TRA.TRA201600.9). The research carried out by E. Rodríguez was supported by the DOC-INIA program funded by INIA-FEDER. We also wish to thank Michael O’Shea for proofreading the text.

Although the behaviour of animals facing the conflicting demands of increasing foraging success and decreasing predation risk has been studied in many taxa, the response of pollinators to variations in both factors has only been studied in isolation. We compared visit rates of two pollinator species, hoverflies and honeybees, to 40 Chrysanthemum segetum patches in which we manipulated predation risk (patches with and without crab spiders) and nectar availability (rich and poor patches) using a full factorial design. Pollinators responded differently to the tradeoff between maximising intake rate and minimising predation risk: honeybees preferred rich safe patches and avoided poor risky patches while the number of hoverflies was highest at poor risky patches. Because honeybees were more susceptible to predation than hoverflies, our results suggest that, in the presence of competition for resources, less susceptible pollinators concentrate their foraging effort on riskier resources, where competition is less severe. Crab spiders had a negative effect on the rate at which inflorescences were visited by honeybees. This effect was mediated through changes in the foraging strategy of honeybees, and could, in principle, be reversed by increasing nectar productivity of inflorescences. Our study shows that both pollinator species responded simultaneously and differently to variations in food reward and predation risk, and highlights the importance of studying the foraging strategies of pollinators in order to fully understand how plant–pollinator interactions are established. (Resume d'auteur)

In order to choose adequate conservation strategies to face the deterioration of natural ecosystems and the decline of species, it is essential to know the spatial distribution of diversity. Here, we use predictive modelling in spiders, which is a group of highly diverse generalist predators that show a great potential as diversity indicators. We built a predictive model of spider species richness within a protected area assessing those environmental factors that have the strongest effect in the distribution of spider species richness. Our results show a strong relationship between spider species richness and landscape descriptors of land cover. We also assessed the importance of the spatial scale to identify patterns of spider diversity and we selected the optimal spatial scale for species richness and composition by a multiscale approach. We found that this relationship in spiders occurs at relatively fine scales, i.e., 220 × 220 m. The multiple linear regression model at the optimal scale explained 82% of the total variance in species richness. We used the Jackknife procedure to validate the model and we obtained a predictive map of spider richness by extrapolating the model to the entire range of the protected area. Our results show that predictive modelling is a useful tool to estimate the spatial patterns of diversity in a widespread group of arthropod generalist predators.

Three new troglobiontic species of the spider genus Cybaeodes Simon endemic to caves in the southeastern Iberian Peninsula are described and illustrated: Cybaeodes indalo sp. n. from Almería, C. dosaguas sp. n. from València and C. magnus sp. n. from Alacant. The new species confirm the presence of Cybaeodes on the Iberian Peninsula and its wide distribution throughout the Western Mediterranean including Algeria, Tunisia, Italy, France, Spain and the islands of Sardinia, Sicily and Mallorca. A record of C. liocraninus (Simon), from an Iberian cave was probably based on misidentified specimens of C. magnus sp. n. C. liocraninus is known only from Algeria and should be removed from lists of the Iberian fauna. In addition, the three new species are clear candidates for protection: they have highly restricted ranges and show a high degree of adaptation to the subterranean environment.

Pollutants and toxic contaminants produced in all parts of the world are transported to remote regions including Antarctica. Tourism, research, and fishing activities on this continent are another source of contamination. Toxic substances affect Antarctic species, and some produced genomic damage to the fauna. The genetic damage can be detected by microscopic observation of erythrocytic nuclear abnormalities (ENAs). We counted the number of ENAs in seven populations of three Pygoscelid penguin species, Adélie (Pygoscelis adeliae), Chinstrap (Pygoscelis antarctica), and Gentoo (Pygoscelis papua), and found important differences among species exposed to the same conditions. ENAs were more frequent in Adélie penguins than in the other two species. Inter-population comparisons within species showed remarkable differences in Adélie and Chinstrap penguins but not in Gentoo penguin. Frequency of ENAs in Adélie penguins was the highest in Yalour Island population, intermediate in King George Island population, and the lowest in Torgersen Island and Avian Island populations. In Chinstrap penguins, the highest number of ENAs was found on Deception Island, and significant differences were found only between Deception Island and King George Island populations. This information will provide baseline data to be used for assessing the evolution of genomic damage of penguins along the Antarctic Peninsula in the future., This study was funded by the Spanish Ministry of Science and Innovation and the European Regional Development Fund under the Projects REN2001-5004/ANT, CGL2004-03148, POL2006-05175, CGL2007-60369 and CTM2011-24427 during writing.

Human activity and specifically tourism has been increasing in Antarctica over the last few years. Few studies have examined the indirect effects of human visits on Antarctic penguin rookeries. This work aims to study the differences between a highly visited (Hannah Point) and a rarely visited (Devil's Point, Byers Peninsula) gentoo penguin rookery on Livingston Island. Our results suggest that potential indirect effects of human impact are observed in gentoo penguins at Hannah Point, a colony heavily visited by tourists. Penguins at Hannah Point showed a higher presence of heavy metals such as Pb and Ni and a higher number of erythrocytic nuclear abnormalities than penguins at Devil's Point. Immunological parameters showed different results depending on whether we consider the cellular response -the number of lymphocytes being higher in penguins from Hannah Point- or the humoral response -the level of immunoglobulins being higher in penguins from Devil's Point. Measurements of corticosterone levels in feathers and heterophil/lymphocyte (H/L) ratio in blood showed lower levels in the heavily visited rookery than in the rarely visited rookery. Finally, we did not detect Campylobacter jejuni, a bacteria potentially transmitted by humans in either of the populations and we did not find any difference in the prevalence of Campylobacter lari between the populations., Centro de Estudios Parasitológicos y de Vectores

Background Sexual cannibalism may be a form of extreme sexual conflict in which females benefit more from feeding on males than mating with them, and males avoid aggressive, cannibalistic females in order to increase net fitness. A thorough understanding of the adaptive significance of sexual cannibalism is hindered by our ignorance of its prevalence in nature. Furthermore, there are serious doubts about the food value of males, probably because most studies that attempt to document benefits of sexual cannibalism to the female have been conducted in the laboratory with non-natural alternative prey. Thus, to understand more fully the ecology and evolution of sexual cannibalism, field experiments are needed to document the prevalence of sexual cannibalism and its benefits to females. Methodology/Principal Findings We conducted field experiments with the Mediterranean tarantula (Lycosa tarantula), a burrowing wolf spider, to address these issues. At natural rates of encounter with males, approximately a third of L. tarantula females cannibalized the male. The rate of sexual cannibalism increased with male availability, and females were more likely to kill and consume an approaching male if they had previously mated with another male. We show that females benefit from feeding on a male by breeding earlier, producing 30% more offspring per egg sac, and producing progeny of higher body condition. Offspring of sexually cannibalistic females dispersed earlier and were larger later in the season than spiderlings of non-cannibalistic females. Conclusions/Significance In nature a substantial fraction of female L. tarantula kill and consume approaching males instead of mating with them. This behaviour is more likely to occur if the female has mated previously. Cannibalistic females have higher rates of reproduction, and produce higher-quality offspring, than non-cannibalistic females. Our findings further suggest that female L. tarantula are nutrient-limited in nature and that males are high-quality prey. The results of these field experiments support the hypothesis that sexual cannibalism is adaptive to females.

[Background] Animals have been hypothesized to benefit from pendulum mechanics during suspensory locomotion, in which the potential energy of gravity is converted into kinetic energy according to the energy-conservation principle. However, no convincing evidence has been found so far. Demonstrating that morphological evolution follows pendulum mechanics is important from a biomechanical point of view because during suspensory locomotion some morphological traits could be decoupled from gravity, thus allowing independent adaptive morphological evolution of these two traits when compared to animals that move standing on their legs; i.e., as inverted pendulums. If the evolution of body shape matches simple pendulum mechanics, animals that move suspending their bodies should evolve relatively longer legs which must confer high moving capabilities., [Methodology/Principal Findings] We tested this hypothesis in spiders, a group of diverse terrestrial generalist predators in which suspensory locomotion has been lost and gained a few times independently during their evolutionary history. In spiders that hang upside-down from their webs, their legs have evolved disproportionately longer relative to their body sizes when compared to spiders that move standing on their legs. In addition, we show how disproportionately longer legs allow spiders to run faster during suspensory locomotion and how these same spiders run at a slower speed on the ground (i.e., as inverted pendulums). Finally, when suspensory spiders are induced to run on the ground, there is a clear trend in which larger suspensory spiders tend to run much more slowly than similar-size spiders that normally move as inverted pendulums (i.e., wandering spiders)., [Conclusions/Significance] Several lines of evidence support the hypothesis that spiders have evolved according to the predictions of pendulum mechanics. These findings have potentially important ecological and evolutionary implications since they could partially explain the occurrence of foraging plasticity and dispersal constraints as well as the evolution of sexual size dimorphism and sociality., This paper has been written under a Ramón y Cajal research contract from the Spanish Ministry of Science and Culture (MEC) to JML and a FPI scholarship (BES-2005-9234) to GC. This work has been funded by MEC grants CGL2004-03153 and CGL2007-60520 to JML and GC, as well as CGL2005-01771 to EM